How Long Does It Take for Canine Dewormer to Work?

Canine dewormer may take up to 6 weeks to completely stop the cycle of infection, as stated by PetMD. Treatment requires two to three applications of dewormer spaced 2 weeks apart.

Worms are a common problem for puppies and adult dogs. It is particularly common in puppies, who do not have a strong immune system. They can even get worms from their mother. So, it is very important to treat puppies and adult dogs with signs of a parasitic infection with dewormer.

There are multiple parasites to be concerned about, but the one that causes most infections is Toxocara canis, or the roundworm. Treatment of this parasite involved giving the dog a dose of dewormer orally, which kills any worms living in the dog's intestines. After 2 weeks, a second dose may be given to kill off worm eggs that have hatched in the meantime.

It is often necessary to give multiple doses, between two to three, of dewormer. Eggs in the dog's body can hatch after the first dose is given, or the dog can reinfect itself when playing in the yard.

If the dog has contracted heartworm, treatment is more prolonged, expensive and dangerous, according to WebMD. The treatment is actually derived from arsenic, and when the worms die off, they can break up into pieces that potentially block the flow of blood to the heart. Dogs receive three injections over a 2-month period. The owner has to keep the dog calm for 6 months after this to prevent further damage from the dying worms. Then, the dog is retested for heartworm. If the tests show the dog is still infected, a second round of treatment is required.